1. Field
The present disclosure relates generally to inspecting objects and, in particular, to inspecting objects using interferometry systems. Still more particularly, the present disclosure relates to inspecting objects using laser interferometry inspection systems.
2. Background
Aircraft are being designed and manufactured with greater and greater percentages of composite materials. Composite materials are used in aircraft to decrease the weight of the aircraft. This decreased weight improves performance features such as payload capacity and fuel efficiency. Further, composite materials provide longer service life for various components in an aircraft.
Composite materials may be tough, light-weight materials created by combining two or more functional components. For example, a composite material may include reinforcing fibers bound in a polymer resin matrix. The fibers may be unidirectional or may take the form of a woven cloth or fabric. The fibers and resins may be arranged and cured to form a composite structure.
Using composite materials to create aerospace composite structures may allow for portions of an aircraft to be manufactured in larger pieces or sections. For example, a fuselage in an aircraft may be created in cylindrical sections to form the fuselage of the aircraft. Other examples include, without limitation, wing sections joined to form a wing or stabilizer sections joined to form a stabilizer.
In manufacturing composite structures, layers of composite material may be laid up on a tool. The layers of composite material may be comprised of fibers in sheets. These sheets may take the form of, for example, without limitation, fabrics, tape, tows, or some other suitable configuration for the sheets. In some cases, resin may be infused or pre-impregnated into the sheets. These types of sheets are commonly referred to as prepreg.
The different layers of prepreg may be laid up in different orientations and different numbers of layers may be used depending on the desired thickness of the composite structure being manufactured. These layers may be laid up by hand or using automated lamination equipment such as a tape laminating machine or a fiber placement system.
After the different layers of composite material have been laid up on the tool, the layers of composite material may be consolidated and cured upon exposure to temperature and pressure, thus forming the final composite structure. Thereafter, the composite structure may be inspected to determine whether inconsistencies are present.
This inspection may be performed using ultrasound testing, eddy current testing, x-ray testing, visual inspections, and other suitable types of testing. In particular, this type of testing results in nondestructive inspection of the object.
This testing may be performed to identify various inconsistencies in the composite structure. For example, without limitation, inconsistencies may include delamination, voids, undesired levels of porosity, foreign object debris, and other types of inconsistencies.
If an inconsistency is identified, the composite structure may be reworked. In some cases, the inconsistency may result in the composite structure being discarded, thus requiring a new composite structure to be manufactured.
One type of nondestructive inspection system is a speckle shearing interferometry inspection system. A speckle shearing interferometry inspection system may be called a shearographic inspection system and may be used to perform inspections for inconsistencies in a composite structure.
This type of inspection system employs shearography, which is an optical inspection technique that measures out of plane displacement in the surface of the composite structure. For example, air entrapped in a disbonded portion of a composite structure may cause a change in the surface of the composite structure. This out of plane displacement may be used to determine the mechanical strain of the composite structure under test.
A shearographic inspection system is configured to detect these types of changes and uses a laser unit as a light source to generate coherent light in the form of a laser beam. The laser beam illuminates the surface of the composite structure. The light from the laser beam may result in a pattern of light being reflected from the surface of the composite structure. This pattern of light is caused by different features on the surface of the composite structure.
Movement is generated in the surface of the composite structure. When an inconsistency is present in the layers of composite material under the surface of the composite structure, movement of the surface of the composite structure may not be uniform. As a result, an identifiable change in the pattern of light reflected from the surface of the composite structure may be detected.
Images of the patterns of light may be generated. The images of these patterns of light may be analyzed to determine whether an inconsistency is present in the composite structure.
Although a shearographic inspection system is useful in identifying inconsistencies in a composite structure, currently available shearographic inspection systems may be more limited in application than desired. The size and complexity of shearographic inspection systems may limit the situations in which this type of inspection system may be used.
Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above, as well as other possible issues.